The strategic utilization of facing layers is investigated as a mechanism to increase the energy absorption in foam liner systems for improving the protective performance of helmets. Energy absorption applications extensively use foams because of their ability to efficiently absorb large amounts of strain energy at low stress levels; however, many deformations are localized to a small volume of the foam available in the system thereby reducing the material system effectiveness. One of these cases occurs as the result of poor fit of helmets. This paper details a systematic computational investigation characterizing the energy absorption of multi-layer material constructions consisting of foam combined with a relatively stiff facing layer. Results obtained reveal that facings provide a mechanism to alleviate the effects of a small deformation area caused by both poor fit and thick comfort foam in helmets, though the facings must have substantial flexural rigidity of [Formula: see text] to improve the energy absorption of the pads. Energy absorption efficiency of the foam-facing system for multiple loading curvatures have been used to quantify the energy absorption improvements of the system provided by the use of higher facing rigidity, especially when the impact is near or past the edge of the pad system.

The PIA specification or MIL requirements for mechanics of parachute canopy fabrics are primarily focused on ultimate strength in quasistatic uniaxial stress conditions. Such a focus overlooks the complex multi-axial, hysteretic, and rate-dependent behavior of fabrics. In this work, we present extensive material data pertaining to a number of canopy fabrics of interest to both NASA and the US Army. The objective is to present the important variations on mechanical behavior measured at conditions as similar to the opening and deployment of parachutes as achievable in the lab. The exposition starts with presenting quantitative analysis of the significance of fabric anisotropy (orthotropy, with substantially low and sensitive in-plane shear flexibility). Fabrics with similar quasistatic strength ratings may have very different and contrasting mechanics, leading to potentially disparate failure modes. We continue by exploring the dissipation of stress work in cyclic loading of the selected fabrics. This could reach nearly half of the input stress work in the first cycle, and although it decreases with each cycle of loading, it continues to be a significant fraction of the stress work. Again, the variation among presumably similar fabrics (i.e. of similar quasistatic strength ratings) is emphasized and associated with finer yet salient features of the textile structure and behavior [1]. We continue by introducing a novel experimental setup capable of evaluating fabric specimens in loading rates that are estimated to mimic opening stages of parachute deployments. While no direct measurement of rates of deformation during opening are available, various computational and experimental estimates point to an intermediate range (1-100/s). Testing samples with reasonable dimensions at these rates, and up to the expected levels of deformation is a significant challenge. Such characterization requires higher displacement speeds than what is ordinarily accessible in standard quasi-static load frames. The intermediate strain rate apparatus design presented in this work is based on a split-Hopkinson bar testing setup, which is modified for testing fabric specimens at rates of 1-100/s under tension. During such a test, the sample deformation is observed with a high-speed camera. It is important to note that via optical observation, the potential interference of gages on the mechanical response of the sample used in direct strain measurement is eliminated. Furthermore, full field and time resolved deformation maps may be determined via Digital Image Correlation (DIC) methodology. From DIC, it is possible to extract the in-plane strain components: axial, transverse, and shear. Force may also be calculated based on the mass and deceleration of the head assembly during the test. Improvements in force measurements will be discussed as the dynamics of the frame is expected to influence the measured response and separation of the two (frame vs. sample) is rather challenging. The experimental setup, and data acquisition / analysis for these tests are a work in progress, with the progressive results providing great insights in effective behavior of canopy fabrics in practice [2]. We further focus the study by selecting two examples of PIA-C-44378 Type IV fabrics. The difference in mechanical behavior of the two candidates is particularly of interest as they essentially could be exchanged based on the same designation. Additionally, we study one such fabric in various stages of manufacturing. This study sheds light on various effects that the fabrication process could have on the final product.

To counter a perceived increase in multi-piece fracturing of wood baseball bats, Major League Baseball implemented standards to regulate the quality of wood used in the making of professional-grade baseball bats. These specifications included a minimum density as a function of wood species and a standard related to slope of grain (SoG). Following the implementation of these specifications in 2008, there was a 65% reduction in the multi-piece failure rate. It is hypothesized that a further reduction in the breakage rate can be realized through the implementation of regulations on allowable bat profiles. In the current work, a parametric study was conducted to develop a quantitative understanding of the relationship between bat durability (i.e., resistance to breaking), SoG, and bat profile, thereby obtaining data to support or refute the hypothesis. Finite element models of the bat/ball impact of four different popular bat profiles were created using LS-DYNA software. Similarities and differences between bat profiles impacted at two relatively vulnerable axial locations are presented and discussed. Lastly, the respective bat durabilities for all of the profiles were compared using a probability analysis that considers the SoG, impact location, impact velocity, and it predicts an in-service bat durability.

It is critical to know the material properties of the fabrics for the construction of aerodynamic decelerator systems that utilize canopy fabrics. With a comprehensive knowledge of material characteristics, it is possible to tune parachute designs in terms of cost and efficiency. Through quasi-static testing of the F-111 (PIA-C-44378) canopy fabric, the salient material behavior has been determined concerning nonlinearity, hysteresis, recovery, anisotropy, and strain-rate dependence.

The significance of the relationship between surface hardness and wood bat durability is currently not well understood. In the current exploratory study, the Janka hardness of maple wood bats with and without a surface treatment was studied. The Janka hardness of each bat from a set of finished wood baseball bats from five different manufacturers was measured at three locations on the radial grain of the barrel region of each bat. Eight maple wood billets were hardness tested at four locations at 1.6-cm increments. All samples were conditioned at 22 ˚ C and 50% R.H. for >2 weeks before testing. The nominal sizes of the billets were 6.4 cm in diameter and 33.7 cm in length. Billets were categorized based on the growth-ring density (wide or tight) and by the grain surface (radial or tangential). Each billet had one of two different proprietary surface treatments consisting of a cross-linked polymer heat treatment developed and applied by Dove Tail Bats. Four of the eight billets were cut down their length such that the testing was conducted on the tangential grain of the wood while the remaining four were tested on the radial grain of the wood. The Janka hardness of the wood was calculated as given in ASTM Standard D1037-12 [1]. Per the wood handbook, the expected Janka hardness values for maple wood are expected to be near 6450 N [2]. A tabulated comparison of the average measured hardness of the five baseball bats and average hardness of billets by surface finish are shared in Table 1. BM1 denotes Bat Manufacturer #1, etc. Note that the billet hardness values are the averages of the respective tested grain surfaces (16 hardness tests each).

A finite element based computational model simulating the standard drop tower test for military helmets was created and used in conjunction with a multi-output Gaussian process surrogate to seek different designs of helmets for improved blunt impact performance. Experimental drop test results were used for the validation of the model’s ability to simulate impact. The influence of foam stiffness, impact velocity, strap tension, as well as pad placement and size on parameters on the peak linear acceleration (PLA) of the headform was investigated for the first time through a surrogate model trained by strategically choosing simulation points. Impact velocity was found to have the greatest effect. The strap tension and foam pad stiffness ranges examined within this sampling plan were found to have less of an effect on the performance of the helmet than the pad size and shape parameters examined. The surrogate modeling approach was used to quantify the influence of design parameters and can lead to not only improved helmet designs but also new data-driven design metrics and testing standards to accelerate the development of TBI-mitigating helmets.

During the 2008 Major League Baseball (MLB) season, there was a perception that the rate at which wood bats were breaking was on the rise. MLB responded by implementing changes to the wood bat regulations that were essentially transparent to the players, e.g., changing the orientation for the hitting surface on maple bats, setting a lower bound on wood density, and reducing the allowable range for the slope of grain (SoG) of the wood used to make bats. These new regulations resulted in a 65% reduction in the wood-bat breakage rate. It is proposed that a further reduction to the multi-piece failure (MPF) rate can be realized by accounting for the role that bat profile plays with respect to bat durability. Durability is defined here as the relative bat/ball speed that results in crack initiation, i.e., the higher the breaking speed, the better the durability. The aim of the current work is to complete a parametric study to investigate if bat profile influences bat durability with respect to SoG. Three bat profiles with very different geometries and volumes are analyzed using the finite element software, LSDYNA®. The mechanical behavior of the wood is modeled using the *MAT_WOOD material model in combination with the *MAT_ADD_EROSION option. The effective wood material properties are varied as a function of wood density and SoG. Results include how varying bat profile and SoG influences bat durability. The study is limited to maple wood bats.

Foams are used in a variety of impact energy absorption applications because of their ability to engage in large deformations under steady load transfer during the cell collapse. Quantification of the energy absorption capabilities of foams, including those resulting from repeated loading and unloading, is critical to both modeling and prototype development of systems utilizing these important materials. This paper details a novel process of characterizing a cross-linked high-density polyethylene foam for its applicability within helmet liners designed for low-velocity blunt impact. The foams are characterized using various forms of compression testing and physical measurements. The analyses include examination of the tangent modulus, strain hardness, energy absorption ideality, and energy absorption efficiency. Together, these analyses identify the regions of changing behavior of the nonlinear impact absorption material system. A case study for the materials is presented, which reveals that the examined high-density polyethylene foam exhibits some of the most efficient impact properties during the first impact. However, this case study also identifies that those impact properties can reduce significantly, e.g. a 55% increase in stress in the case of a 0.50 strain-level deformation in the first impact, for a subsequent impact after only a 120 s rest period. The novel combination of testing and analysis presented within this paper enables the developer of a foam energy absorption system to advance their interrogation of foams for repeated large strain deformations and temperature variations.

Bat durability is defined as the relative bat/ball speed that results in bat breakage, i.e., the higher the speed required to initiate bat cracking, the better the durability. In 2008, Major League Baseball added a regulation to the Wooden Baseball Bat Standards concerning Slope-of-Grain (SoG), defined to be the angle of the grain of the wood in the bat with respect to a line parallel to the longitudinal axis of the bat, as part of an overall strategy to reverse what was perceived to be an increasing rate of wood bats breaking into multiple pieces during games. The combination of a set of regulations concerning wood density, prescribed hitting surface, and SoG led to a 30% reduction in the rate of multi-piece failures. In an effort to develop a fundamental understanding of how changes in the SoG impact the resulting bat durability, a popular professional bat profile was examined using the finite element method in a parametric study to quantify the relationship between SoG and bat durability. The parametric study was completed for a span of combinations of wood SoGs, wood species (ash, maple, and yellow birch), inside-pitch and outside-pitch impact locations, and bat/ball impact speeds ranging from 90 to 180 mph (145 to 290 kph). The *MAT_WOOD (MAT_143) material model in LS-DYNA was used for implementing the wood material behavior in the finite element models. A strain-to-failure criterion was also used in the *MAT_ADD_EROSION option to capture the initiation point and subsequent crack propagation as the wood breaks. Differences among the durability responses of the three wood species are presented and discussed. Maple is concluded to be the most likely of the three wood species to result in a Multi-Piece Failure. The finite element models show that while a 0°-SoG bat is not necessarily the most durable configuration, it is the most versatile with respect to bat durability. This study is the first comprehensive numerical investigation as to the relationship between SoG and bat durability. Before this numerical study, only limited empirical data from bats broken during games were available to imply a qualitative relationship between SoG and bat durability. This novel study can serve as the basis for developing future parametric studies using finite element modeling to explore a large set of bat profiles and thereby to develop a deeper fundamental understanding of the relationship among bat profile, wood species, wood SoG, wood density, and on-field durability.

This paper reports the outcomes of a series of two Concussion Research Workshops held in Lowell, MA, USA. The workshop examined the state-of-the-art in concussion research, research challenges and the future directions of research within the following three core topic areas: (A) Concussion Prevention Techniques & Technology, (B) Concussion Diagnosis, and (C) Treatment of Concussions. Concussions are a form of traumatic brain injury caused by an impact and are a growing concern among athletes and those who are involved with sports. Recent years have led to increasing awareness and research related to concussions with limited definitive understanding of the specific mechanism and pathology. Technology is beginning to take on an important role in the prevention, diagnosis and treatment of concussions. Currently, sensors provide data about the impact and the athlete. However, sensors and better protective equipment can enable an effective monitoring and thus protection of athletes. Only when a more definitive understanding of the injury mechanism is achieved, can sensors and protective equipment design contribute to effective monitoring and protection of athletes.

This paper reports the findings from the 2016 Wind Energy Research Workshop held in Lowell, MA. The workshop examined the state-of-the-art in wind energy research within the following three core topic areas: (A) Wind Turbine Design and Manufacturing including: blades, towers/foundations and nacelle, (B) Wind Farm Development including: offshore installations/siting, flow characterization and loads/waves/wind characterization, and (C) Wind Farm Operations including: controls, power production, wind farms, sensing, diagnostics, testing, structural health monitoring, reliability, energy storage, the grid and power transmission. Research challenges and future directions were discussed and are reported for each sub-topic area.

Batting cage pitching machines are widely used across the sports of baseball and softball for training and recreation purposes. The balls are specifically designed for the machines and for the environment to ensure high durability and typically do not have seams. Polymeric foam balls are widely used in these automated pitching machines for batting practice in a cage environment and are similar in weight and size compared with the regulation balls used in leagues. The primary objective of this paper is to characterize the polymeric balls and their interaction with the pitching machine. The paper will present measured ball properties and measured relationships between various pitching machine parameters such as wheel speed, and the ratio of wheel speeds on the ball exit velocity and rotation. This paper will also characterize some of the effects of wear on the baseballs and wheels from their prolonged use.

To assist in developing a database of wood material properties for the finite element modeling of wood baseball bats, Charpy impact testing at strain rates comparable to those that a wood bat experiences during a bat/ball collision is completed to characterize the failure energy and strain- to-failure as a function of density and slope-of-grain (SoG) for northern white ash (Fraxinus americana) and sugar maple (Acer saccharum). Un-notched Charpy test specimens made from billets of ash and maple that span the range of densities and SoGs that are approved for making professional baseball bats are impacted on either the edge grain or face grain. High-speed video is used to capture each test event and image analysis techniques are used to determine the strain-to-failure for each test. Strain-to-failure as a function of density relations are derived and these relations are used to calculate inputs to the *MAT_WOOD (Material Model 143) and *MAT_EROSION material options in LS-DYNA for the subsequent finite element modeling of the ash and maple Charpy Impact tests and for a maple bat/ball impact. The Charpy test data show that the strain-to-failure increases with increasing density for maple but the strain-to-failure remains essentially constant over the range of densities considered in this study for ash. The flat response of the ash data suggests that ash-bat durability is less sensitive to wood density than maple-bat durability. The available SoG results suggest that density has a greater effect on the impact failure properties of the wood than SoG. However, once the wood begins to fracture, SoG plays a large role in the direction of crack propagation of the wood, thereby determining if the shape of the pieces breaking away from the bat are fairly blunt or spear-like. The finite element modeling results for the Charpy and bat/ball impacts show good correlation with the experimental data.

In a response to reverse the trend of a perceived increase in multi-piece failures (MPFs) of wood baseball bats in Major League baseball games, the Office of the Commissioner of Baseball implemented changes to the Wooden Baseball Bat Specifications (WBBS) in December 2008. These changes introduced bat-supplier regulations that outlined strict quantitative requirements for wood quality and instituted a third-party inspection of professional wooden baseball bats for the 2009 season. Additional changes to the WBBS for the 2010, 2011, and 2012 seasons targeted increasing the density of the wood used to make maple bats, thereby increasing the minimum breaking strength of the wood allowed for these bats. By the completion of the 2014 season, these changes had driven a 65% reduction in the rate of MPFs per game relative to the 2008 season. It is hypothesized that the rate of MPFs can be further reduced if regulations on the allowable geometries of the taper region for the bats used by MLB teams are implemented. To develop a fundamental understanding of the relationship among (1) the angle of the taper (2) the starting point of the taper along the length of the bat, and (3) wood density, a series of generic bat profiles that were subjected to bat/ball impacts was investigated using LS-DYNA. In this paper, the results of these bat/ball impact simulations are shared, and a summary of the various combinations of these geometric parameters on bat stress and strain is presented. The durability information gained from these generic bat profiles is then used to give guidance in understanding why certain bat profiles used in professional baseball have relatively high rates of MPFs while other profiles exhibit a relatively low rate of MPFs. (C) 2016 Published by Elsevier Ltd.

Changes in the Wooden Baseball Bat Standards (WBBS) by the Office of the Commissioner of Baseball in cooperation with the MLB Players Association in response to recommendations made by a task force comprised wood and baseball science experts have produced a 65% reduction in the rate of multi-piece failures (MPFs) of bats since 2008. It is hypothesized that the rate of MPFs can be further reduced if regulations on the allowable geometries of the taper region for the bats used by MLB teams are implemented in the WBBS. To develop a fundamental understanding of the relationship among (1) the angle of the taper region of the bat, (2) the starting point of the taper along the length of the bat, and (3) wood density, a series of actual and generic bat profiles was investigated using LS-DYNA for bat/ball impacts. In this paper, the results of these bat/ball impact simulations are shared, and a summary of the various combinations of these geometric parameters on bat stress and strain is presented. The durability information gained from these studies is then used to develop an understanding of why certain bat profiles used in professional baseball have relatively high rates of MPFs while other profiles exhibit relatively low rates of MPFs.

Finite element models of wood baseball bats are a valuable tool to explore the relationship between bat profile and bat durability. However, for such finite element models to be credible, the material models must capture the mechanical response of the wood under consideration. In the current research, a comprehensive experimental program was conducted to characterize the mechanical behavior of maple and ash woods for the range of densities used to make major-league quality baseball bats. The test program included (1) four-point bend testing to determine elastic moduli and strength and (2) Charpy testing to determine strain to failure as a function of strain rate and wood density. The material parameters were subsequently calibrated by completing finite element simulations of the Charpy tests in LS-DYNA using the MAT_WOOD material model. This paper describes the experimental characterization program used to determine material parameters of maple and ash wood species for use in finite element simulations of wood baseball bats.

Major League Baseball (MLB) currently has few restrictions on the bat profiles allowed for use during gameplay. Although current multi-piece failure (MPF) rates are at their lowest in years, there is still room for further improvement by regulating the bat profiles allowed in games. The influence of bat profile tapering was analyzed utilizing finite element models of various known profile geometries to determine the effect on bat durability. LS-DYNA simulations were processed for profiles over a range of maple wood densities that would be currently allowed by MLB regulations. This paper will describe the various modelling studies conducted to determine the factors that comprise a bat profile of good durability. The results of the modelling are compared to on-field data of bat failures during gameplay of known profiles used by MLB players. A profile scoring formula is proposed that is a combination of bat geometrical characteristics and bat wood density. This score is shown to be a good predictor of the relative durability of a given set of bat configurations.

The putting of a golf ball requires control of the speed and direction and an understanding of the interaction between the ball and the putting green by the golfer. The putt can involve a combination of the ball flying over, skidding across, and rolling on the putting green. This study used finite element analysis as a tool to investigate these behaviors, and this paper documents the results for putts with different initial velocities. The finite element analyses were performed in LS-DYNA using a viscoelastic material model for the turf and an elastic material for the golf ball and club head. A high-grade artificial putting turf was characterized by its compressive stiffness in a Universal Testing Machine and displacement of a golf ball resting on turf. The static and dynamic friction between the golf ball and artificial turf were investigated. The ball velocity and deceleration resulting from different putts were examined to help in the characterization of the behavior of the turf. The finite element model will be used in future studies to determine the optimal putter loft and rise angles to achieve consistent putts.

The bats used in Major League Baseball (MLB) are required to be turned from a single piece of wood. Northern white ash had been the wood of choice until the introduction of hard maple in the late 1990s. Since the introduction of maple to the game, there was a perceived increase in the rate of bats to exhibit multiple piece failures (MPF)—both ash and maple. These failures introduced a new aspect to the game that can be a significant factor during play, i.e. pieces of bats going into the field of play, thereby distracting fielders while reacting to the batted ball. Observations of bat breakage in the field and lab testing of bats in controlled conditions have shown the bat durability is a function of wood quality and bat profile. Wood quality is described by the density and the slope of grain of the wood used in the bat. The density and the slope of grain determine the effective strength of the wood. The bat profile is described by the variation in the diameter of the bat along its length. The wood densities and bat profiles which are preferred by players, are typically in direct contradiction with what makes for a durable bat. In this paper, the finite element method is used to develop calibrated models of the breaking of wood bats in controlled lab conditions. The modeling approach is then used to explore how bat profile influences bat durability and what potential changes can be made in bat profile to satisfy player desires while increasing bat durability.